Nelson U.S. Pat. No. 4,398,238 describes an adjustable focus flashlight having a reflector mounted in the head, in which the focus is adjusted by turning the head on the flashlight body, as is well-known in the art. Nelson shows a switch module in the body which holds the bulb. He teaches retaining the focus adjustment with a helical spring disposed partly in the flashlight body and partly within the head. One end of the spring is seated on the outer, or rearward, surface of the reflector, and the other flat end is seated on the switch module. As Nelson points out, the seat on the switch module is flat and relatively slick, so the spring can easily rotate with respect to the module as the head is turned. If this were not so, according to Nelson, the spring might be more effective than desired in retaining the position of the head, and could even prevent a desired focus of the flashlight beam from being accomplished. Alternatively, Nelson points out, if twisting the head were accompanied by twisting of the spring, then the spring would tend to return to its initial position rather than retaining it in the desired position of adjustment. Obviously, then, using the seat on the switch module to support the spring prevents the storage of a spare bulb near the end of the module.
My invention, on the other hand, eliminates the spring, and provides an easily accessible spare bulb near the end of the switch module. Instead of the spring, I provide a replaceable switch unit threadably connected to the head and the battery unit, said unit having an O-ring that frictionally engages part of the head, to retain the focus adjustment.